Sensor to body calibration is a key requirement for capturing accurate body movements in applications based on wearable systems. In this paper, we consider the specific problem of estimating the positions of multiple inertial measurement units (IMUs) relative to the adjacent body joints. To derive an efficient, robust and precise method based on a practical procedure is a crucial as well as challenging task when developing a wearable system with multiple embedded IMUs. In this work, first, we perform a theoretical analysis of an existing position calibration method, showing its limited applicability for the hip and knee joint. Based on this, we propose a method for simultaneously estimating the positions of three IMUs (mounted on pelvis, upper leg, lower leg) relative to these joints. The latter are here considered as an ensemble. Finally, we perform an experimental evaluation based on simulated and real data, showing the improvements of our calibration method as well as lines of future work.

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This paper presents the design and development of STants, a low-cost, wearable system for monitoring lower body movements in long-term training sessions. Multiple miniaturized inertial measurement units (IMUs) are integrated into a pair of pants and socks using textile cables. This results in a lightweight and easy to use platform providing comfortableness and maximal movement flexibility for the user. A customized firmware for energy-efficient data acquisition, in addition to a selection of low-power components extends the autonomous operation time compared to traditional approaches. Power consumption and data quality (in terms of estimated joint angles) are assessed in different experiments, showing the potential use of the proposed platform within personal training scenarios.

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